The interest in utilization of lignin in various applications has steadily grown over the years with the main driving force to find a sustainable alternative to mineral oil-based products. An area where the intrinsic properties of lignin i.e. the existence of a cross-linked network, can be harnessed most efficiently is the utilization of lignin to reinforce a multitude of polymeric materials such as urethane-based networks and polymers.
In DE 19,548,350, DE 19,648,724, U.S. Pat. Nos. 4,918,167, 3,546,199, 3,654,194, WO 2013,113,462 as well as the set of publications by Glasser and co-workers [1-8] and more recently by Cateto et al. [9-10], Gandini et al. [11] Nadji et al. [12], Li et al. [13], Xue et al. [14], and Arshanitsa et al. [15, 16] alkoxylation of lignin has been attempted. However, these approaches so far encounter some serious drawbacks;    1) All scientific publications as well as all relevant patents report significant degrees of homopolymerization of propylene oxide under the reaction conditions applied [WO 2013,113,462]. As a consequence, the degree of process control for the polyol synthesis is severely reduced and the formulation latitude is more or less lost due to difficulties to assess how much homopolymer is formed.    2) At the reported reaction conditions, self-condensation of the lignin macromolecule structure is always present leaving non-soluble fractions in the resulting polyol [WO 2013,113,462]. This requires additional filtration step(s) in the polyol manufacturing process.
US 2,013,255,216 claims a modified lignin comprising phenolic groups masked with propylene oxide. However the claimed compositions are produced in aqueous environment which is severely limiting the application in the production of polymers, especially those polymers comprising water-reactive monomeric species such as urethanes.
In conclusion, none of the aforementioned publications and patents describes a satisfactory technology for producing lignin polyols.
A dispersion containing lignin is also disclosed in WO2013179251
Therefore there exists a need for a method to produce lignin polyols that are liquid, smell neutral, without homopolymers and/or precipates that require unwanted additional processing steps (such as filtration, extraction etc.).